This invention relates to a multi-cylinder engine control system, and more particularly to an improved feedback control system for a multi-cylinder engine.
In the interest of providing good fuel economy and effective exhaust emission control, resort has been made to feedback control systems for controlling the air/fuel ratio. By employing an exhaust sensor or a combustion product sensor, it is possible to determine if the mixture is rich or lean. Thus, by using the output of this sensor, the fuel supply can be controlled so as to maintain the desired air/fuel ratio.
One difficulty with this type of system is that the sensors employed are somewhat fragile and are prone to contamination. This problem is particularly acute in conjunction with two-cycle engines. With a two-cycle engine it is desirable to sample the combustion products almost directly in the cylinder so as to avoid dilution during the scavenging cycle. However, the two-cycle engines normally employ separate lubricating systems, and the sensor may be subjected not only to fuel contamination, but also contamination by the lubricant.
The problem is particularly acute during the original start-up mode. As is well known, it is the normal practice to run an overly rich mixture to assist in starting, particularly with a cold engine. When this is done, however, then the sensor may be contaminated and the eventual following feedback control may be erratic or inaccurate.
It is, therefore, a principal object of this invention to provide an improved feedback control system for an engine.
It is another object of this invention to provide an improved feedback control system for a multi-cylinder engine.
It is a yet further object of this invention to provide a feedback control system for a multi-cylinder engine wherein the sensor is protected during starting from contamination by either fuel and/or lubricant.